You can use gray water for irrigation only if it is captured in the home....ie. a bucket in your shower, under a sink, etc. It is "illegal" to pump or re-route the gray water from the septic tank according to the dept.of public health. I believe the maximum is 5 gallons a day if I remember correctly. With the amount of homes in metro Atlanta on septic, it would be an epidemic waiting to happen if they allowed it. Hope this helps.